1. Field of the Invention
The present invention relates to a method for manufacturing a fiber type coupler by fusing and elongating a plurality of optical fibers.
2. Related Background Art
FIG. 1 is a block diagram which shows a related background art manufacturing method of the fiber type coupler. The related background art manufacturing method is now explained. Two optical fiber wires of 50 cm length are prepared. Each of the optical fiber wires has a plastic jacket and an RIV (room temperature vulcanized silicon) coating. The coatings of the optical fiber wires are partially removed, and the optical fibers 1 having the coatings partially removed are contacted to each other and they are fixed by fixing members 2 in the contacted state. In this case, a photo-sensor 3 and a power meter 4 are connected to one end of each optical fiber, and a light source 5 is connected to the other end.
Then, the contacted optical fibers are heated by a burner 6, and a monitoring light from the light source 5 is sensed by the photo-sensors 3 and measured by the power meters 4 in order to monitor a split ratio at the coupler area. When the split ratio reaches a desired value, the elongation is stopped and a protective member is molded to form the fiber type coupler (see Japanese PCT published Patent (A) 60-501427).
A vertical adjuster for adjusting a vertical position of the optical fiber and a horizontal adjustor for adjusting a horizontal position are used, and the optical fibers are positioned vertically and horizontally. (See Japanese Patent Application 59-88166).
However, in the two-direction positioning method described above, there is a difference among tensile force applied to the optical fibers when they are fixed to an optical fiber fixing member. (Refer to Japanese Laid-Open (KOKAI) Patent Application 63-118705)
FIG. 2 is a perspective view which illustrates an affect of the tensile force in the fusing process. FIG. 2A shows a fiber type coupler manufactured under a constant tensile force applied during the fusing process, and FIG. 2B shows a fiber type coupler manufactured under different tensile force applied during the fusing process. When the applied tensile forces are different, the coupler is bent at a fusing region A because the tensile forces are released in the molten state, and a twist is generated. The bend or twist at the fusing region A increases an insertion loss of the fiber type coupler. Further, since the bending state is not constant, a reproducibility of the fiber type coupler is low and hence a yield is low.
In order to eliminate the above drawbacks, a manufacturing apparatus has been improved. (See Japanese Laid-Open (KOKAI) Patent Application 63-118705). In this apparatus, in the position adjustment process of the manufacture of the fiber type coupler, the optical fibers are fixed to a movable table to which a constant force is applied so that the optical fibers are positioned under a uniform tensile force applied to the optical fibers. In this manner, the bend and twist at the fusing area are reduced.
However, in order to keep the tensile force constant, means for balancing the tensile forces is additionally required in the conventional manufacturing apparatus. As the diameter of the optical fiber is reduced, or as the number of wires increases, it becomes harder to keep the tensile forces uniform and a higher precision control is required. As a result, the cost of the apparatus rises.
In the related background art manufacturing method of the fiber type coupler, the photo-sensor must be connected to one end of the optical fiber. As a result, the workability in the mass production is poor.